Chapter 11 How Does the Internet Work?

How Important is this Chapter to Understanding How to Use a Computer? 7 or 8 on a scale of 1 to 10

How Important is this Chapter to understanding how a computer works? 7 or 8 on a scale of 1 to 10

What is the Internet? The Internet involves millions of computers connected in a complex way to a maze of local and regional networks. NOTE that when referring to THE internet, you should capitalize the first letter. When referring to a network that is configured similarly the word internet is not capitalized.

Origins of the Internet 1969 –Department of Defense established, ARPANET, an experimental network connecting 4 research computers. 1980’s –National Science Foundation –Only scientific, research and academic institutions –NO commercial traffic Late 1990’s –Commercialization of the Internet.

Other Developments… 1989 – via CompuServe and MCI Mail 1991 –ISP’s - Internet Service Providers (AOL, and others) –NAP’s - National Access Points National and International standards organizations

Standards for the Internet Internet Society (ISOC) Internet Engineering Task Force (IETF) Internet Architecture Board (IAB) Internet Corporation for Assigning Names and Numbers (ICANN)

Ownership and Operation No one owns the Internet. Revenue is required to offset the hardware, software, and maintenance costs. The cost must be covered by users. –Organizations (ex. U of S) –Individuals (ex. I pay for my connection at home)

What’s the difference between the Internet and the World Wide Web? Intuitive difference –WWW is the multimedia portion of the ‘net. –Images, sounds, videos, animation, etc. Technical difference –Web is the part of the Internet that contains Web Servers and Web sites.

Internet Addresses Two designations: –Internet Protocol Address (IP number) 32 bit address consisting of 4 parts represented decimally is an example Each of the 4 numbers has a range from 0 to 255. These numbers are assigned by outside agency. E.g. Everything at the U of S starts –Domain Name Descriptive name for IP address Also assigned by “outside agency” Specifically scranton.edu was assigned to the University’s Web site. The rest was chosen by the University. Upper level domains (.edu in this example) are restricted in their use.

More Addresses Ethernet Address (or Media Access Control Address) –48 bit address (6 bytes) that uniquely identifies each networking component in your computer. –For example, my computer has both a wired and a wireless network connection, so it has two MAC addresses, one for each device. –Each MAC address refers to a specific piece of hardware. –Theoretically no two pieces of hardware have the same MAC address. BUT, it’s rumored that certain government agencies have special hardware that can change MAC addresses to fool communication.

How does your computer go to the correct Web site? EXAMPLE at the U Browsers must use IP addresses not domain addresses. So the first step is to translate the domain address to an IP address. You type in into your browser. The browser goes to the University’s Domain Name Server to look up the name. Since the name ends in scranton.edu, the name server knows that you are seeking a Web server on campus. So IT looks up the IP address and sends your browser that info and your browser goes to that site.

How does your browser go the correct Web site (continued)? Example at the U (continued) You type into your browser Your browser goes to the University’s DNS to look up the name. It recognizes that the name does NOT end in scranton.edu and so it knows that that site in NOT on campus. So the U’s DNS sends the request up the line to a “higher level” DNS which recognizes the location and sends back the IP addresss.

IP Addresses Two types: Dynamic and Static Static IP addresses remain the same. So a particular IP address will be associated with a particular domain name always. Dynamic IP addresses change. Each time you turn your computer on it will get a “new” IP address from a list of available addresses. It’s sort of like a parking permit. The permit doesn’t guarantee you a particular parking space just the right to park in a particular general area. The Dynamic IP address is obtained from a program called DHCP (dynamic host configuration protocol) which is located on the computer that you hook to when you connect to the Internet.

What Browser should I use? There are many choices: –Internet Explorer –Firefox, Mozilla, Netscape –Opera –The above three are all available in Windows and except for IE all are also available on mac and unix. –Safari is the built in browser for macintosh –Galeon and Konqueror are standards for unix. Which one should you use? –Which ever one you like, but if you have a windows computer you should keep IE available since lots of Web programmers build sites that are not compatible with other browsers.

How do Browsers work? They transfer documents according to hypertext transfer protocol (HTTP) or one of its derivatives. The pages are written in a programming language called HTML (HyperText Markup Language). You’re familiar with this from your Web page creation. There are other newer versions of HTML which can also be used. Scripting languages such as JavaScript can run on your browser to make a page interactive. PHP is a scripting language that runs on the server.

Scripting Languages (continued) Client side processing (using JavaScript or the equivalent) lets your computer do the work and therefore is faster to use than sending things to Web sites and having the work done there and sent back. It’s also more dangerous since it can be used to attack your computer. It’s typically used for mouseovers and similar effects. Server side processing (such as PHP and ASP) is typically used for transmitting forms.

Summary Every computer on the Internet has an address. This address can be given in two ways: IP address and perhaps domain address. Computers must use IP addresses to communicate and typically for people domain addresses are more convenient so there has to be a way to translate from domain to IP. This is done using Domain Name Servers. IP addresses are assigned by external organizations. So are domain names. Some of the addresses can be chosen locally.

Summary (continuted) Network hardware also has an address which is unique to each device. Web sites are downloaded using HTTP protocol Web sites are created using HTML or equivalent languages with client side interactivity using JavaScript or equivalent and server side programming using several different languages. There are many browsers available. But there are also many incompetent Web programmers, so you need to have access to Internet Explorer for at least some Web sites.

Terminology Backbone Bandwidth Client-Side processing Domain Address Dynamic IP address DHCP DNS HTML ISP IP address MAC address NAP Node Server-side processing Static IP address Top-level domain